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394

FATTY SUBSTANCES  (GENERAL METHODS)

assumed by the oil after shaking for about two minutes and of its colora-
tion after the mixture has been kept for 20 minutes in a boiling water-bath.

Olive, almond, hazel-nut and arachis oils retain their natural colour
or become somewhat paler. Olive oil may, however, sometimes assume
a greenish tint, especially in the cold. If these oils are rancid, they may
turn orange-coloured.

Sesame, cottonseed, beechnut, linseed, walnut, colza, and mustard oils,
etc., change to orange or brownish red.

3.  BRULLE'S REACTION.   In a test-tube 10 c.c. of the oil, o-i gram of
dry, finely powdered egg-albumin and 2 c.c. of pure nitric acid prepared
as for Hauchecorne's reaction are carefully and uniformly heated until the
acid begins to boil, the whole being then shaken somewhat and the heating
continued until the albumin is completely dissolved, this occurring in a
few seconds.

During the boiling with the acid and albumin, olive oil becomes almost
entirely decolorised and after cooling forms a more or less turbid liquid of
a straw-yellow colour which persists for a long time, but after 24 hours it
sets to a solid mass of the same colour. Similar behaviour is shown by
arachis, almond and walnut oils.

Seed-oils, however, become deep yellow (colza, sesame) or orange-red
to brown (cottonseed, poppyseed, maize, beechnut, linseed, etc.).

4.  BELLIER'S REACTION.   5 c.c. of the oil or filtered  fused  fat, 5 c.c.
of pure, colourless nitric acid of D = 1-4 and 5 c.c. of a cold, saturated
solution of resorcinol in benzene are introduced into a graduated cylinder
with a ground stopper and shaken for about 10 seconds, the colour being
observed during the shaking and immediately afterwards (10-15 seconds).

In place of the benzene solution of resorcinol, a 0-1% ethereal solution
of phloroglucinol (Kreis) may be used.

Seed oils in general, and especially sesame", cottonseed, poppyseed,
linseed, maize (corn oil), soja-bean and colza oils, give colorations varying
from pink to red to violet to brown (with phloroglucinol more distinctly
red).

This reaction serves more particularly to detect vegetable seed oils in animal
fats (lard), in lard oil, in foot oils, and also in olive oil, since these animal fats
and oils and olive oil give no appreciable coloration, at any rate within 5-20
seconds. After this time all oils and fats give colorations.

Practice with oils and fats of known origin is necessary in order to distin-
guish pure oils and fats from mixtures by this reaction.

With oils which have been subjected to long exposure to light or to heating
in the air, the reaction fails.

24.   Elaidin Test

10 grams of the oil and 5 c.c. of nitric acid (D 1-40) are shaken in a test-
tube for two minutes, I gram of mercury being then added and dissolved
by energetic shaking; the tube is then left at rest for about 30 minutes.

With pure olive oil a solid white or yellowish mass is obtained and similar
behaviour is shown by arachis, almond and lard oils. Sheep's foot oils,
and mustard, colza, ravison, sesame", cottonseed and other semi-drying 2 c.c. of nitric acid prepared from 3 vols. of pure nitric